A typical LCD device includes an LCD panel, and a backlight module mounted under the LCD panel for supplying light beams thereto. The backlight module is generally classified into one of two types—a direct type or an edge type—according to the position in which a light source is installed in a backlight unit of the backlight module.
In the case of a direct type backlight module, the light source may be one or more elongate lamps or a plurality of light emitting diodes (LEDs). A light spreading plate and a light reflection plate are installed at top and bottom sides of the light source respectively. The light spreading plate is located directly under the LCD panel. Accordingly, some light beams are substantially directly output from the light source to the LCD panel positioned above the light spreading plate, and other light beams reflected from the light reflection plate are then substantially directly output to the LCD panel.
FIG. 5 is a schematic, side cross-sectional view of a conventional backlight module. The backlight module 10 includes a diffusion sheet 11, a plurality of lamps 12, and a reflective plate 13. The lamps 12 are disposed between the diffusion sheet 11 and the reflective plate 13. The diffusion sheet 11 and the reflective plate 13 are thin, and each of the lamps 12 is elongate.
When the size of the LCD device increases, the size of the lamps 12 used therein should also increase. If the lamps 12 are unduly long, they may not be secure and may be prone to break. This is particularly the case when the LCD device is subjected to vibration or shocking during use or transportation.
FIG. 6 shows another kind of conventional backlight module. The backlight module 20 has a structure similar to that of the backlight module 10, and includes a diffusion sheet 21, a reflective plate 23, and a plurality of lamps 22 disposed between the diffusion sheet 21 and the reflective plate 23. The backlight module 20 further includes a plurality of posts 24 disposed between the reflective plate 23 and the diffusion sheet 21, to ensure that a gap with a predetermined distance is formed between the reflective plate 23 and the diffusion sheet 21. The lamps 22 are fixed to corresponding fasteners 26. The fasteners 26 tightly and securely fasten the lamps 22 in the backlight module 20. This helps prevent the lamps 22 from sustaining damage when the backlight module 20 is subjected to vibration or shock during use or transportation.
FIG. 7 shows reflective optical paths in the backlight module 20. Some of light beams (not shown) emitted by the lamps 22 directly transmit to the diffusion sheet 21. Other light beams emitted by the lamps 22 transmit to the diffusion sheet 21 after being reflected by the reflective plate 23. The light beams then pass through the diffusion sheet 21 to illuminate an associated liquid crystal display panel.
However, a majority of the light beams are transmitted to areas of the diffusion sheet 21 directly above the lamps 22, whereas a smaller quantity of the light beams are transmitted to areas 25 of the diffusion sheet 21 that are generally between each two adjacent lamps 22. Moreover, the fasteners 26 block transmission of some of the light beams emitted by the lamps 22. Thus light intensity distribution in the areas directly above the lamps 22 is greater than light intensity distribution in the areas 25 generally between the lamps 22. This uneven light intensity distribution at the diffusion sheet 21 typically prevents the backlight module 20 from attaining a highly uniform light intensity distribution.
Accordingly, what is needed is a backlight module that can overcome the above-described deficiencies.